Using two-dimensional gel electrophoresis (2DE), we have constructed an atlas showing the location (on polyacrylamide gels) and relative concentration of a number of different proteins from 25 distinct neuroanatomical regions of the male rat brain. The regions examined included cortical areas as well as nuclei from the hypothalamus, amygdala, thalamus, forebrain and hindbrain. Proteins were separated by 2DE, stained with silver and quantitated by computerized densitometry. Some proteins were found to be present in constant amounts in all brain areas examined, others were found to vary somewhat in concentration and some (approximately 10%) varied widely (greater than 10-fold) in concentration among the different brain regions. Using this map, we have extended these observations by examining the effect of the tricyclic antidepressant desmethylimipramine (DMI) and the neurotransmitter depleting agent reserpine on proteins from the hippocampus and parietal cortex. Repeated administration of DMI caused a reduction in the apparent concentration of two proteins in both brain region examined. In contrast, repeated reserpine administration caused an apparante increase in the concentration of both these proteins in the hippocampus, but no change in the parietal cortex. A third protein was elevated in concentration in the hippo-campus by repeated DMI administration, and reduced in concentration by repeated reserpine administration. In all cases, acute drug administration was found to be without effect. This is significant in view of the fact that chronic DMI and reserpine have been shown to cause down and regulation, respectively, of the Beta-adrenergic receptors. We will pursue the possibility that these proteins may be part of the catecholamine receptor.